A satellite ground system receives telemetry values from a satellite sent to space, extracts necessary information from the telemetry value, and monitors the state of the satellite. Also, the satellite ground system transmits commands from the ground to the satellite. Therefore, when fault occurs in the satellite ground system, the satellite may not be able to perform an assigned mission because the telemetry received from the satellite can be lost and a wrong command can be transmitted to the satellite. That is, since the satellite ground system should be able to transmit a telecommand for recovery when an unexpected incident happens in the satellite or when the fault occurs, the satellite ground system needs to maintain a robust state. Accordingly, a backup system of the satellite ground system is important.
To maintain robustness of the satellite ground system, conventional satellite ground systems form cold-backup and hot-backup mechanism by dualizing devices for the fault and an abnormal state. The cold-backup method is operating a secondary ground system when a primary ground system has the fault. The hot-backup method simultaneously drives the primary/secondary systems and switches them with each other in real-time.
When a cold-backup device detects fault in a device of the primary system, the cold-backup device stops to use the primary device and uses a secondary device. Since there is a time gap between the cancellation of the operation of the primary ground system and the restart of the operation of the secondary ground system, the cold-backup device has a problem that data can be lost while the devices are switched and the satellite ground system cannot be processed in real-time.
A conventional hot-backup device prevents data loss by dualizing hardware into primary/secondary devices, and when the fault occurs, switching the primary/secondary systems with each other to replace the faulty device. However, since the conventional hot-backup device does not have an appropriate switching mechanism and it does not have a function for determining a simple fault, the switching may occur frequently even when fault occurs temporarily. Also, since primary/secondary devices are simultaneously used, operation equipment becomes large and it is not possible to separate one system out of the other for repair. Although data are not lost as much as they are in the cold-backup, data loss cannot be perfectly prevented in switching.
Although the satellite ground system is dualized, the conventional method can not perfectly prevent data loss. There is also a problem that switching is carried out even when fault occurs temporarily or a data transmission error occurs.